U.S. patent number 4,112,677 [Application Number 05/763,770] was granted by the patent office on 1978-09-12 for thrust spoiler for turbofan engine.
This patent grant is currently assigned to Avco Corporation. Invention is credited to Joseph R. Kasmarik.
United States Patent |
4,112,677 |
Kasmarik |
September 12, 1978 |
Thrust spoiler for turbofan engine
Abstract
A multiplicity of retractable spoilers are placed at spaced
angular intervals within the annular duct which carries the bypass
airstream in a turbofan engine. Deployment of the spoilers into the
bypass annular duct causes a partial blockage of the airstream.
This results in a decrease in thrust from the engine without any
change in throttle setting.
Inventors: |
Kasmarik; Joseph R. (Stratford,
CT) |
Assignee: |
Avco Corporation (Stratford,
CT)
|
Family
ID: |
25068764 |
Appl.
No.: |
05/763,770 |
Filed: |
January 31, 1977 |
Current U.S.
Class: |
60/226.1;
239/265.37 |
Current CPC
Class: |
F02K
3/06 (20130101) |
Current International
Class: |
F02K
3/06 (20060101); F02K 3/00 (20060101); F02K
003/06 () |
Field of
Search: |
;60/226A,226B,226R,229,230,262 ;239/265.13,265.37 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Garrett; Robert E.
Attorney, Agent or Firm: Gelling; Ralph D.
Claims
I claim:
1. In a turbofan engine having a driven fan rotating in an annular
duct which is a continuation of the engine air intake, said fan
providing an airstream which is divided, one part of said airstream
being fed to the engine compressor of the gas producer unit, the
other part of said airstream being ducted through an annular bypass
which surrounds the turbine, apparatus for reducing the thrust
output of the bypassing portion of the engine airstream at low
throttle settings, said apparatus comprising:
a multiplicity of retractable spoilers placed at spaced apart
intervals circumferentially around the outer wall forming the
annular duct carrying the bypass airstream the active area of each
of said spoilers being a generally rectangular plate; and
means for positioning said spoilers to an actuated and a retracted
position, said retracted position being that which recesses the
generally rectangular plate of each of said spoilers into the outer
wall enclosing said bypass ducting allowing air to freely flow
therethrough when the spoilers are retracted, said actuated
position being that which deploys said spoilers into the bypass air
passage, said deployment being such that the forward facing side of
each generally rectangular plate portion of each of said spoilers
lies in a plane which is perpendicular to the axial centerline of
said gas producer section; the deployment of said spaced apart
spoilers being for the purpose of both partially blocking airflow
in the bypass air passageway and at the same time creating
turbulent air flow conditions within the passageway.
2. The invention as defined in claim 1 wherein each of said
retractable spoilers comprise in combination:
a pair of supports extending radially outward from the outer wall
enclosing said bypass ducting, each of said pair of supports
locating the placement of a thrust spoiler station, each such pair
of supports lying in a plane perpendicular to the axial centerline
of said gas producer section, the outer ends of each of said
supports being journaled, the journals of each pair of said
supports being coaxially aligned;
a hinge pin rotatably mounted in said journaled supports; and
a generally rectangular plate having mounting bracket connections
for attaching said plate to said hinge pin, said mounting bracket
connections including means providing for pivotal motion of said
plate around said hinge pin from a retracted to an actuated
position.
3. The invention as defined in claim 2 wherein the means providing
for pivotal motion of said plate around said hinge pin includes a
reversible motor having a gear drive.
4. The invention as defined in claim 2 wherein the width of each of
said plates is dimensioned to match the cross-sectional height of
the turbofan bypass ducting.
5. The invention as defined in claim 2 wherein the supports,
extending radially outward from the outer wall enclosing said
bypass ducting, have the centerlines of their journaled outer ends
lying in a single plane, said plane being perpendicular to the axis
of said gas producer section.
6. The invention as defined in claim 5 wherein adjacent thrust
spoiler stations are mechanically linked by flexible cable means
serially connecting one hinge pin with the next.
7. The invention as defined in claim 1 wherein there are at least
four retractable spoilers.
Description
BACKGROUND OF THE INVENTION
The forward fan high bypass engine incorporates a gas producer unit
which is furnished air from a compressor that is driven by a
turbine. Extending forward of the compressor is a shaft which
through reduction gearing drives a large diameter ducted fan. The
fan rotates in an annular duct which is a continuation of the air
intake. The airstream accelerated by the fan is divided. One part
of the airstream (primary air) is fed to the compressor to provide
an air supply for the gas producer unit. The other part of the
airstream (secondary air) bypasses the gas producer through an
annular duct which surrounds the turbine. In some turbofan engines
this portion of the airstream is ejected directly as a "non-mixed"
exhaust. In other engines the bypassing airstream is "mixed" with
the gas-generator exhaust at the core engine jet nozzle. The object
of the bypass system is to combine the good operating efficiency
and high thrust capability of a turboprop and the high speed, high
altitude capability of a turbojet while achieving lower fuel
consumption.
This invention provides a means for reducing the thrust output of
the bypassing portion of the engine airstream at low throttle
settings. The requirement to reduce thrust materializes when an
aircraft equipped with high bypass fan engine(s) is waiting in line
on a taxi strip or airport apron. The thrust of a high bypass
engine, even at idle power setting, can be sufficient to cause the
aircraft to move forward unless the flight crew maintains constant
brake pressure. This task, when the aircraft encounters long
waiting periods for take-off clearance, increases crew fatigue and
interferes with normal pre-flight check lists and
communications.
A prior art system of engine thrust control is described on page
118 of R. A. Fry's book titled "The Principles and Construction of
Aircraft Gas Turbines", published by Sir Isaac Pitman and Sons,
Ltd., London, 1960. In the system described by Fry, there is a ring
of non-rotating guide vanes placed in front of the mechanically
driven fan. The angle of incidence of these guide vanes can be
varied to suit changing operating conditions.
There is a drawback to this approach which my invention overcomes.
In the system described by Fry, varying the pitch of the entry
vanes changes the amount of air going to both the gas producer and
the bypass ducts. With the airstream going to the gas producer
choked down the pilot will have to change throttle settings to
maintain efficient conditions in the turbine. In addition, the
inlet vanes must be anti-iced, which adds considerable complexity
to the engine system. Using my invention, the air intake of the gas
producer section is not disturbed when the thrust spoilers are
activated. Thus, no change in throttle setting of the engine is
required.
SUMMARY OF THE INVENTION
A multiplicity of retractable flaps are placed in the outer wall of
the air bypass ducting in a turbofan engine. When deployed into the
bypass air passageway the flaps act as thrust spoilers in that they
both partially block the air passageway and at the same time create
turbulent flow conditions within the passageway. The flaps are
positioned downstream from the air inlet to the gas producer
section of the turbine. This precludes performance degradation of
the gas producer section of the engine when the flaps are deployed.
In the unit reduced to practice the thrust spoiler flaps were
positioned so that the hinge pin of each flap was in a plane
perpendicular to the axis of the turbine. Collectively, the hinge
pins and extensions thereof formed a circumferential ring around
the periphery of the bypass duct. This allowed the flaps to be
mechanically interconnected so that they could be actuated in
synchronism. The flaps were positionable in two states. In one
state they were recessed in and flush with the outer wall of the
bypass duct. In the other, they were rotated 90.degree. around the
hinge pin from the recessed position so as to interrupt air flow in
the bypass duct to the maximum extent possible. This means
90.degree. rotation of the flap around the hinge pin from the
retracted to the actuated state. The flaps were symmetrically
positioned around the bypass passageway. For the case where four
thrust spoilers were used, each was spaced so that their center
lines were at 90.degree. intervals. When six thrust spoilers were
used, 60.degree. intervals between center lines was selected.
Actuation and retraction of the thrust spoiler flaps can be
achieved by either gear or crank arm drive means. Through
mechanical linkages one actuating mechanism can be made to
simultaneously operate all or several thrust spoilers.
Alternatively, each thrust spoiler might have its own actuating
drive source.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a turbofan engine with partial
cutaways showing the gas producer section surrounded by a bypass
duct in which there is a thrust spoiler;
FIG. 2 is a top view of one of the thrust spoilers as it appears
when seen from the outside of the bypass passageway; and
FIG. 3 is a side view of one of the thrust spoilers taken along
line 3--3 of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1, turbofan engine 10 is shown positioned within nacelle
12. Brackets 14 connect nacelle 12 to engine 10, and allows the aft
portion of the nacelle to be removed to provide access to spoiler
components. The turbofan engine 10, shown in cutaway view in FIG.
1, is typical of high bypass ratio units having a single
front-mounted ducted fan stage 16. Fan stage 16 rotates in annular
duct 18 which is a continuation of the engine air intake. The
stream of air accelerated by fan stage 16 is divided. "Primary" air
enters passageway 22, passes over fixed guide vanes 67, and enters
the compressor. "Secondary" air passes over fixed guide vanes 20
and is fed through annular duct 27 for eventual discharge at nozzle
26 as a cold gas stream.
In the FIG. 1 arrangement, fan stage 16 supercharges compressor
stages 28 and 30. Air from compressor stage 30 is forced radially
outward by impeller blades 32 so as to pass through diffuser 34.
High pressure air from diffuser 34 flows through orifices into
combustor 36. Fuel enters combustor 36 through nozzles 38. The hot
gases from the combustor drive turbine blade stages 40 and 42.
Power absorbed from the hot gas stream by turbine stages 40 and 42
is used to drive the compressor stages via tubular shaft 44.
Hot gases leaving turbine stage 42 pass through fixed guide vanes
46 and on into turbine stage 48. Power absorbed by turbine stage 48
serves to drive input fan stage 16 via shaft 52 and reduction
gearing 54. Hot gases leaving turbine stage 48, and exiting at
tailpipe 50, provide a small portion of overall engine thrust.
Recessed in outer wall 58 of annular duct 24 there are a
multiplicity of thrust spoilers 60. Thrust spoilers 60 can be
actuated to the 60a position (see dashed line position near top
center of FIG. 1). In the actuated position 60a, the thrust
spoilers partially block the bypass air flow passage, greatly
reducing output thrust at annular cold jet nozzle 26. However,
actuation or retraction of thrust spoilers 60 causes very little
change in the operation of the gas producer section of the turbine.
This is because the thrust spoilers 60 are downstream from the
inlet passageway 22 which furnishes air to the gas producer. The
net result is that use of my invention allows reduction of engine
thrust, through activation of thrust spoilers, with the engine at
minimum operating speed.
FIGS. 2 and 3 show one of the thrust spoilers 60 in more detail.
Thrust spoiler 60 comprises a generally rectangular plate 62 to
which are fastened mounting brackets 64 and 65. Mounting brackets
64 and 65 are pivotally mounted via hinge pin 66 to supports 68 and
69. Supports 68 and 69 are attached to the outer side 58 of the
annular bypass duct 24. Mounting brackets 64 and 65 may be attached
to plate 62 by any appropriate means such as, for example, spot
welding. In a like manner, supports 68 and 69 may be attached to
wall 58 by welding or other well-known methods. It is to be
understood that brackets 64 and 65 are both firmly attached to
hinge pin 66 and that hinge pin 66 is readily rotatable in supports
68 and 69. Fluting of the hinge pin 66 in the areas enclosed by
mounting brackets 64 and 65 is one way to accomplish firm
attachment. Use of coil spring 70 which at one end is anchored in
hole 72 formed in hinge pin 66 and at the other end is anchored to
support mount 69, provides a restoring torque to keep the thrust
spoiler 60 in the recessed position shown in FIG. 2.
Power to actuate the thrust spoilers 60 may be implemented in any
of several ways. An electric motor method is shown in FIGS. 2 and
3. Worm gear 74 (see FIG. 2) is driven by worm 76 (see FIG. 3).
Worm 76 is powered by the shaft of reversible electric motor 78. As
hinge pin 66 (see FIG. 3) is turned through 90 degrees in the
clockwise direction, thrust spoiler 60 assumes the activated
position 60a, shown in dashed lines. Stopping electric motor 78
after it has turned the proper number of revolutions in either
direction is readily accomplished by the use of microswitches which
are actuated by a control arm clamped to hinge pin 66.
Other means for actuating thrust spoilers 60 could be used. For
example, a hydraulic motor, a hydraulic piston, or an air piston
could be used. The piston-type actuators would require that there
be a crank arm connected to hinge pin 66 instead of the worm gear
74 shown in FIG. 2.
Whatever means of actuation is used, the need is to rotate plate 62
on command about hinge pin 66 such that it advances from contact
with recessed lip 59 to actuated position 60a. Later, when the
pilot wants to achieve maximum thrust for take-off, issuance of a
counter-command signal should cause plate 62 to retract to the
recessed position. It is important to note that whatever system is
used for activation, all would incorporate a fail-safe system for
spoiler retraction as engine thrust is increased beyond a pre-set
level.
By mechanically linking the entire complement of thrust spoilers
together, it has been found that several thrust spoilers can be
driven from a single motor. This was accomplished by
interconnecting one thrust spoiler station with the next, by means
of a series of flexible cables 82 (see FIG. 2). These are serially
attached from one hinge pin 66 to the next by use of collars 80.
The cable transmits torque from one thrust spoiler 60 to the next
even though adjacent thrust spoilers are angularly displaced by the
radius of curvature of duct wall 58.
In summary, my invention provides a pilot with thrust spoilers
which can be actuated to reduce the tendency of the high bypass
turbofan equipped aircraft to creep forward on a taxi strip or
flight ramp even though the speed of the engines has been reduced
to ground idle. Further, the thrust spoilers of my invention can be
actuated without need for additional adjustment of engine throttle
parameters.
While I have shown only one embodiment of the thrust spoiler, it is
understood that numerous variations in configuration are possible
within the scope of the present invention. It should be apparent to
those skilled in the art that the invention can be practiced in
other forms without departing from its spirit and scope.
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